The invention relates to rotating antenna arrays with plural antenna elements which can be individually rotated to change the phase of the signal of the individual antenna elements, altering the direction of the main lobe of the antenna.
Current aircraft-satellite communications require an antenna design which is capable of phase scanning. On small aircraft, another requirement is that the physical dimensions of the design be small. Conventional phase scanned arrays use digitally controlled diode phase shifters that introduce substantial losses in the RF path. These losses degrade the antenna gain and increase the antenna noise temperature resulting in a very low gain/temperature characteristic for a given antenna size.
Future aeronautical satellite communications antennas will serve multiple purposes such as providing voice communications to the cockpit and cabin, data and internet services, and live video entertainment. The transmission of multiple simultaneous voice and data carriers can produce intermodulation products that may interfere with other navigation and communications systems on the aircraft and on the ground.
Transmission and reception over the Inmarsat network from aircraft demands an antenna whose beam can be scanned over most of the upper hemisphere, allowing the beam to be directed towards the satellite regardless of the aircraft orientation. This beam steering can be achieved using mechanically steered antennas. These are usually mounted inside the top of the stabilizer where size limitations are critical. Access to the tail is quite difficult on large commercial aircraft due to the size and weight of the tail-fin radome and the height of the tail.
Current technologies in mechanically steered arrays do not allow for maximum flexibility in phase scanning and satellite tracking. One technology, disclosed in U.S. Pat. No. 4,427,984 issued to Anderson attempted to solve this problem. Anderson discloses an antenna array with rotatable antenna elements. The phase of the antenna elements are changed to move the lobe of the array to point towards a satellite or signal source. However, Anderson does not disclose how the whole array may be rotated to track a satellite in two planes from a mobile platform. As such, Anderson is only suitable for tracking in a single plane and cannot be used to scan a beam in both elevation and azimuth as required for mobile satellite communications.
Other technologies have tried to provide platforms for other antenna types. Specifically, dish antennas have been tried as the antenna element for numerous antenna platforms. German Patent DE 4 405 644 issued to Braun et al., UK Patent GB 2266 996 issued to Racal Research Limited have both tried this approach. Unfortunately, such an approach leads to complex mechanical systems which require time consuming and labour intensive maintenance. In addition, such antennas are very tall and are thus not suitable for mounting in restricted spaces.
Another approach, shown in U.S. Pat. No. 4,771,290 issued to Storey, uses a rotating platform for a ranging system. However, Storey does not mention using such a platform for an antenna system for aircraft use.
From the above, there is a need for a low profile antenna drive system which is capable of tracking a satellite from a mobile platform. Such an antenna should be readily adaptable for aircraft use or for use with any other moving vehicle and must be of a low cost, reliable design.
The current invention provides a steerable antenna array and a drive mechanism for an antenna array mounted on a moving vehicle. The antenna array is mounted on a disc having two motors which, cooperatively, rotate the disc in the azimuthal plane and rotate a number of antenna elements mounted on the disc about the boresight axis of the elements. By rotating the antenna elements as aforesaid, the main lobe of the array may be scanned towards a satellite in the elevation plane. To track a moving source from a moving vehicle, one of the motors rotates the disc as a whole, thereby scanning the beam in the azimuth plane. Each antenna element is positioned at an angle to the vertical so that, by rotating the disc to face the direction of the signal source, such as a satellite, and rotating selected elements, the main lobe of the antenna can be painted at the source, and a better signal can be obtained.
In a first embodiment, the current invention provides a drive mechanism for rotating multiple rotatable antenna elements mounted on a rotatable pallet having a first side and a second side. The mechanism comprises a main motor for rotating the rotatable antenna elements about the boresight axis, a secondary motor for rotating the pallet, and rotating means for rotating the rotatable antenna elements. The rotating means is coupled to the main motor and to each rotatable antenna element.
In a second embodiment, the current invention provides a drive mechanism for rotating multiple antenna elements mounted on a first side of a pallet rotatable about an axis. The mechanism comprises a rotation mechanism for rotating said rotatable antenna elements, a main motor for rotating said rotatable antenna elements and coupled to at least a portion of said rotatable antenna element through the rotation mechanism, and a secondary motor for rotating the pallet. Also included in the mechanism are a plurality of shafts mounted on a second side of said pallet, each of the shafts being rotatable about its longitudinal axis with the axis being parallel to the pallet. Further included are a plurality of shaft gears, each shaft gear being mounted on a shaft such that a longitudinal axis of a shaft gear is parallel to the longitudinal axis of the shaft and such that rotation of the shaft causes rotation of the shaft gear, a plurality of antenna gears, each antenna gear being mounted on a distal end of a rotatable antenna element, the distal end protruding through a second side of the pallet, and at least one primary transmission means coupled to the main motor and to at least one of said shafts. Each shaft gear is in contact with an antenna gear such that a rotation of a shaft gear causes rotation of an associated antenna gear and a rotation of an antenna gear causes rotation of an antenna element. Activation of the main motor causes at least one primary transmission means to cause at least one of said shafts to rotate.
In a third embodiment, the current invention provides a mechanism for rotating multiple antenna elements mounted on a first side of a pallet rotatable about an axis. The mechanism comprises a main motor for rotating said rotatable antenna elements, a secondary motor for rotating the pallet, and a plurality of slots in the pallet. The rotating means includes a slider pallet located adjacent a second side of the pallet with the slider pallet being rotatable about a slider pallet axis. Also included in the rotating means are a plurality of slider mounts mounted on the first side of the pallet with each slider mount being slidably mounted inside a slot and a plurality of slider cords, each slider cord being wrapped around a portion of a rotatable antenna element. Each slider cord is attached to a slider mount such that slidably moving a slider mount within its associated slit causes its associated rotatable antenna element to rotate. The rotating means further includes a plurality of slider cars mounted on the slider pallet, each of said slider cars being coupled to at least one slider mount, first coupling means to couple the main motor to the slider pallet, and second coupling means to couple the secondary motor to the pallet. The axis of the pallet and the slider pallet axis are substantially collinear. The main motor is coupled to the slider pallet for rotating the slider pallet about the slider pallet axis and the secondary motor is coupled to the pallet for rotating the pallet about the pallet axis. Rotating the pallet and the slider pallet at different rotational speeds causes the rotatable antenna elements to rotate.